Lignans are a class of plant secondary metabolites ubiquitously distributed in the plant kingdom (Non-Patent Document: Umezawa, T. (2003) Phytochem. Rev. 2, 371-390). Some lignans have useful biological activities and are used as drugs or health foods. For example, main furofuran-type lignans contained in Sesamum indicum of the family Pedaliaceae are known to have functions including antioxidative properties, improvement of lipid metabolism, protection of liver function, etc. and are commercially available (Non-Patent Document 1: Nakai, M., et al. (2003) J. Agri. Food Chem. 51, 1666-1670; Non-Patent Document 2: Tsuruoka, T. et al. (2005) Biosci. Biotech. Biochem. 69, 179-188).
On the other hand, podophyllotoxins, which are anti-tumor lignans of allyl tetralin lactone type contained in the root of Berberidaceae Podophyllum peltatum (American May apple), have a cell division inhibitory activity and are used as carcinostatic agents and for development of novel carcinostatic agents (Non-Patent Document 3: Ayres, D. C. and Loike, J. D. (1990) Lignans: Chemical Biological and Clinical Properties. Cambridge Univ. Press, Cambridge, U.K.). Also, numerous lignans are considered to be metabolized in vivo, after their uptake, into enterolactone which has a female sex hormone-like activity.
As such, the usefulness of lignans is becoming clear. In contrast, information of genes for catalytic enzymes in lignan biosynthesis is limited (Non-Patent Document 4: Davin, L. B. and Lewis, N. G. (2003) Phytochem. Rev. 2, 257-288).
Lignan biosynthesis has been studied mainly in Forsythia intermedia, Berberidaceae Podophyllum peltatum and Linum usitatissimum, and starts from pinoresinol which is a furofuran lignan synthesized through oxidative polymerization of coniferyl alcohol that is one of monolignols. It is shown in Sesamum indicum that pinoresinol is converted into sesamin by forming two methylenedioxy bridges in pinoresinol by cytochrome P450 enzyme CYP81Q1 and its metabolite sesaminol is further glucosylated (Non-Patent Document 5: Noguchi, A., et al (2008) Plant J. 54, 415-427).
In the biosynthesis pathway of lignans with a lactone ring, pinoresinols are metabolized by pinoresinol-lariciresinol reductases (PLR) to lariciresinol and then secoisolariciresinol (Non-Patent Document 4). Secoisolariciresinol is further converted into matairesinol by secoisolariciresinol dehydrogenase (SIRD).
The metabolic pathway of lignans with a lactone ring subsequent to matairesinol requires to go through a plurality of enzyme reactions to reach podophyllotoxin glycoside. However, some enzyme activities are merely reported but any execution enzyme has not been isolated (Non-Patent Document 6: Sakakibara, N., et al (2003) Org. Biomol. Chem. 1, 2474-2485).
Anthrissus sylvestris is known to contain lignans with a lactone ring such as yatein, podophyllotoxin, etc. in the leaves and roots. It is further demonstrated by administration experiments with labeled lignans that yatein is biosynthesized via thujaplicatin, 5-methylthujaplicatin and 4,5-dimethylthujaplicatin (Non-Patent Document 6).